As artificial blood vessels with large and medium diameters, woven and knitted tubes of polyesters and drawn tubes made of polytetrafluoroethylene are widely clinically applied, and found to exhibit good patency even though some problems remain to be solved. However, as artificial small caliber blood vessels of less than 6 mm in inner diameter to be used for coronary bypass and peripheral arterial repair of limbs, no satisfactory products are available yet because of the obstruction due to thrombus, and autologous venous transplantation is applied. So, attempts to develop artificial small caliber blood vessels by various methods are being pursued. A major tendency in these methods is to maintain artificial anti-thrombogenic property for a long time. For example, a segmented polyurethane tube known as an anti-thrombogenic material or a material coated with a heparinized material, etc. is used. However, these materials are used with consideration given only to the maintenance of anti-thrombogenic property, and no consideration is given to the affinity with cells. So, the invasion of cells into the substrate has been little expected. Therefore, if a long period of time has passed after implantation, a tissue mainly consisting of vascular endothelial cells called pannus growing from the anastomosed portion floats partially in blood without adhering to the artificial blood vessel wall, and this suddenly obstructs the artificial blood vessel. It is known that such a case often occurs. It was reported that even artificial blood vessels prepared by drawing polytetrafluoroethylene tubes which are clinically widely used as about 6 mm artificial blood vessels caused the pannus obstruction since they were designed under the same concept.
Furthermore, for patches used for repairing hearts and large arteries, it can happen that since it takes time for the inner surface of such a patch to be covered with vascular endothelial cells, thrombus is formed on the surface and liberated to obstruct and infect peripheral blood vessels.
On the other hand, the attempt to immerse a highly porous artificial blood vessel in albumin and to autoclave it for using albumin as a covering of the artificial blood vessel can be easily used by the surgeon during an operation and can more positively inhibit the bleeding from the artificial blood vessel than the so-called pre-clotting fill the voids of an artificial blood vessel with the patient's thrombus, and so is increasingly applied.
An artificial blood vessel covered with crosslinked albumin has some anti-thrombogenic property, since the substrate covered with albumin is hydrophilic and since albumin has negative charges in the body. However, recently it has been found that if such an artificial blood vessel of 6 mm or less, especially 4 mm or less in inner diameter is implanted, the anti-thrombogenic property of the crosslinked albumin alone is insufficient to inhibit the early thrombogenesis after implantation and to maintain patency.
The artificial small caliber blood vessels of less than 6 mm in inner diameter prepared by the above mentioned methods are insufficient in anti-thrombogenic property, and also in patency because of abnormal pannus evolution. Furthermore, patches which are slow to healing and allow thrombogenesis cause peripheral blood vessels to be obstructed and infected.
The object of the present invention is to provide implantation materials which exhibit excellent patency even when used as artificial small caliber blood vessels of less than 6 mm in inner diameter.